Shaft having outer teeth for transferring torque between hydraulic machines arranged coaxially behind one another

ABSTRACT

In a shaft ( 19 ) having outer teeth ( 18 ) for transferring torque between hydraulic machines ( 1, 2 ) arranged coaxially behind one another, especially hydraulic pumps of a steering device, in which an inner wheel ( 7; 8 ) provided with teeth ( 9; 10; 15; 16 ) on the inside and outside moves around the inside of a toothed ring ( 3; 4 ) having inner teeth ( 5; 6 ) and engages with the teeth ( 5; 6 ) of the toothed ring ( 3; 4 ), and the teeth ( 18 ) of the shaft ( 19 ) engage without relative rotation in the inner teeth ( 15; 16 ) of the inner wheels ( 7, 8 ), in order to simplify manufacture and assembly of the shaft and to avoid noise, the thickness of the teeth ( 18 ) of the shaft ( 19 ) or of the inner teeth ( 15; 16 ) of the inner wheels ( 7, 8 ), measured on the reference circle, is greater than the width, measured on the reference circle, of the gaps into which those teeth ( 18; 7; 8 ) engage, with the result that the flanks of the teeth ( 18 ) of the shaft ( 19 ) come into contact securely with the flanks of the inner teeth ( 15; 16 ) of the inner wheels ( 7, 8 ), and the shaft ( 19 ) has slots ( 20 ) in both end portions between at least some of its teeth ( 18 ) and is hollow at least in the end portions that are provided with the slots ( 20 ).

[0001] The invention relates to a shaft having outer teeth for transferring torque between hydraulic machines arranged coaxially behind one another, especially hydraulic pumps of a steering device, in which an inner wheel provided with teeth on the inside and outside moves around the inside of a toothed ring having inner teeth and engages with the teeth of the toothed ring, and the teeth of the shaft engage without relative rotation in the inner teeth of the inner wheels.

[0002] In order to increase the output of a hydraulic machine, especially hydraulic pumps of a steering device that serve as metering pumps, it is known from DE 196 07 064 C2 to operate two relatively small hydraulic machines in parallel. For that purpose there is used a shaft having outer teeth, which connects the two hydraulic machines with one another by bringing the teeth of the shaft into engagement with the inner teeth of the inner wheel. The two hydraulic machines are driven in customary manner by an inserted shaft (also called a Cardan shaft) having outer teeth which also engage with the inner teeth of one of the two inner wheels. If it is desired, for example in a metering pump of the type mentioned, to increase further the total pump capacity or displacement, for example displacement to 1250 cm³, it is difficult to make or produce the inner wheels (even in the case of two hydraulic machines connected in parallel, each having only one half of the desired total output so as to be able, where possible, to use relatively small hydraulic machines already present) and also the shaft connecting the two hydraulic machines with sufficient precision that the teeth of the inner wheels cooperate with the teeth of the shaft without play, in order to avoid the generation of noise. Conversely, on engagement of the teeth of the inner wheels with the teeth of the shaft, a force fit might occur owing to the low production tolerances that would not be met with sufficient precision in the case of such large components, in which case it would be extremely difficult to assemble the shaft with the inner wheels.

[0003] The problem underlying the invention is to provide a shaft of the type mentioned at the beginning that enables simple and economical manufacture, that is easy to assemble and even so provides play-free connection of the hydraulic machines.

[0004] The problem is solved according to the invention in that the thickness of the teeth of the shaft or of the inner teeth of the inner wheels, measured on the reference circle, is greater than the width, measured on the reference circle, of the gaps into which those teeth engage, with the result that the flanks of the teeth of the shaft come into contact securely with the flanks of the inner teeth of the inner wheels, and the shaft has slots in both end portions between at least some of its teeth and is hollow at least in the end portions provided with the slots.

[0005] In that solution, the teeth of the shaft come into contact without play with the inner teeth of the inner wheels. The shaft can be assembled easily, however, because at least at the ends of the shaft the slots enable the teeth of the shaft to yield resiliently in the hollow chamber of the shaft and the teeth of the shaft and inner wheels that engage with one another come into resilient contact with one another. The teeth of the inner wheels and of the shaft do not need to be manufactured with low tolerances. It is only necessary to ensure that the tooth thickness, measured as an arc length on the reference circle, of the teeth engaging in the gaps between the other teeth is slightly greater than the width of the gaps between the other teeth.

[0006] Preferably the thickness of the teeth of the shaft is slightly greater than that of the inner teeth of the inner wheels.

[0007] The shaft can then be provided with an annular groove near each of its ends in the region of its slots. Those annular grooves increase the resilience of the regions of the ends of the shaft provided with teeth.

[0008] Moreover, the inner teeth of the inner wheels can be formed in adjacent end portions of the inner wheels. The inner teeth of the inner wheels thus do not need to be constructed over the entire axial length of the inner wheels.

[0009] The invention will be described hereinafter in greater detail with reference to a preferred embodiment, in conjunction with the drawings, in which:

[0010]FIG. 1 is a front view of a portion of two hydraulic machines in the form of hydraulic pumps connected by a shaft according to the invention;

[0011]FIG. 2 is an axial section of FIG. 1,

[0012]FIG. 3 is an end view of a shaft according to the invention,

[0013]FIG. 4 is the section IV-IV of FIG. 3, and

[0014]FIG. 5 is the section V-V of FIG. 4.

[0015]FIGS. 1 and 2 represent a portion of two hydraulic machines 1 and 2 in the form of hydraulic pumps constructed as metering pumps of a hydraulic steering unit of a motor vehicle. The hydraulic machines 1 and 2 each comprise, respectively, a toothed ring 3 and 4 having inner teeth 5 and 6 and an inner wheel 7 and 8 (displacing wheel) having outer teeth 9 and 10. By means of holes 12 that are in alignment with the gaps between the teeth 5 and 6, an intermediate disk 11 connects the spaces delimited by the teeth 5 and 9 and by the teeth 6 and 10, in dependence on the relative position of rotation of the toothed rings 3, 4 and inner wheels 7, 8. The hydraulic machines 1 and 2 are connected by means of screws (not shown), which are passed through axial bores 13 in the toothed rings 3 and 4, the intermediate disk 11 and a plate 14 that covers the hydraulic motor 4 on one side.

[0016] The inner wheels 7 and 8 are provided on the inside, in adjacent end portions, with teeth 15 and 16, with which there engage outer teeth 18 of a shaft 19 that connects the hydraulic machines 1 and 2 coaxially. The height of the teeth 15 of the inner wheel 7 varies from tooth to tooth (see FIG. 1) as does the height of the teeth 16 of the inner wheel 8 (FIG. 2).

[0017] The shaft 19 is hollow throughout its axial length. It is also possible, however, for the shaft to be hollow only in its end portions. The thickness of its teeth 18, measured as an arc length on the reference circle, is slightly greater than the width of the gaps, measured as an arc length on the reference circle, of the inner teeth 15, 16 of the inner wheels 7 and 8, with the result that the flanks of the teeth 18 of the shaft 19 come into contact securely with the flanks of the inner teeth 15, 16 of the inner wheels 7 and 8. The thickness of the teeth 18 of the shaft 19 can thus be slightly greater than that of the inner teeth 15, 16 of the inner wheels 7, 8. More precisely, the thickness of the teeth 18 of the shaft 19 is slightly greater than the width of the gap between the teeth 15, 16 of the inner wheels 7, 8, the thickness of the teeth and the width of the gaps between teeth being measured as arc lengths on the reference circle of involute toothing of the teeth. Conversely, it is also possible for the thickness of the teeth 15, 16 to be slightly greater than the width of the gaps between the teeth 18. Put more simply, the thickness of the teeth engaging in the teeth gaps is greater than the nominal dimension of the width of the teeth gaps.

[0018] The shaft 19 also has in both end portions, between at least some of its teeth 18, axial slots 20 that are open towards the ends of the shaft 19 and that pass through the wall of the shaft 19 radially, which slots are spaced apart from one another at identical angles. Owing to the slots 20, it is possible for the parts of the shaft 19 that lie between the slots, together with the teeth 18 formed on those parts, to bend resiliently radially inwards as a result of the contact pressure between those teeth 18 and the inner teeth 15, 16 between which the teeth 18 engage, so avoiding a force fit despite the greater dimension. This facilitates assembly of the shaft 19 with the inner wheels 7, 8.

[0019] The ability of the portions of the teeth 18 that engage with the teeth 15, 16 to bend is still further increased by the fact that the shaft 19 is provided with an annular groove 21 near each of its ends in the region of its slots 20. Moreover, there is play between the tip circle of the teeth 18 lying between the annular grooves 21 and the axial centre of the shaft 19 and the root circle of the teeth 15, 16 of the inner wheels 7 and 8. The diameter of the tip circle of the axially outer teeth 18, on the other hand, is only slightly greater than the diameter of the root circle of the teeth 15, 16.

[0020] The intermediate disk 11 engages in an axially central annular groove 22 of the shaft 19 by means of projections 23 that project radially inward (FIG. 2), which projections are arranged to pass through the gaps between the teeth 18 of the shaft 19 during assembly and then, after rotation of the intermediate disk 11 by half the spacing of the teeth 18, to come to rest behind the teeth 18. Thereafter the screws are introduced through the bores 13.

[0021] The teeth 18 of the shaft 19 engage only in an end portion of the axial length of the teeth 15, which end portion lies closest to the facing ends of the inner wheels 7 and 8. A toothed ring gear provided at the end of an inserted shaft (also called a Cardan shaft) is then introduced, from the left-hand side in FIG. 2 through the hollow chamber of the inner wheel 7, into the portion of the teeth 15 that is left free by the teeth 18. The hydraulic machines 1 and 2, insofar as they are in the form of hydraulic pumps, are then driven by means of that inserted shaft and the shaft 19. It would also be possible, however, to operate the hydraulic machines 1 and 2 as hydraulic motors by feeding in a hydraulic fluid, which hydraulic motors would then drive a work apparatus by means of the inserted shaft.

[0022] To provide the inner wheels 7 and 8 with teeth 15, 16 only in their adjacent end portions, which are relatively short in comparison with the total length of the inner wheels 7 and 8, as shown in FIG. 2, has the advantage that it is easier to manufacture the teeth 15, 16. Alternatively, it would also be possible to extend the teeth 15, 16 over the entire axial length of the inner wheels 7 and 8. 

1. Shaft (19) having outer teeth (18) for transferring torque between hydraulic machines (1, 2) arranged coaxially behind one another, especially hydraulic pumps of a steering device, in which an inner wheel (7; 8) provided with teeth (9; 10; 18) on the inside and outside moves around the inside of a toothed ring (3; 4) having inner teeth (5; 6) and engages with the teeth (5; 6) of the toothed ring (3; 4), and the teeth (18) of the shaft (19) engage without relative rotation in the inner teeth (15; 16) of the inner wheels (7; 8), characterized in that the thickness of the teeth (18) of the shaft (19) or of the inner teeth (15; 16) of the inner wheels (7; 8), measured on the reference circle, is greater than the width, measured on the reference circle, of the gaps into which those teeth (18; 7; 8) engage, with the result that the flanks of the teeth (18) of the shaft (19) come into contact securely with the flanks of the inner teeth (15; 16) of the inner wheels (7; 8); and the shaft (19) has slots (20) in both end portions between at least some of its teeth (18) and is hollow at least in the end portions that are provided with the slots (20).
 2. Shaft according to claim 1, characterized in that the thickness of the teeth (18) of the shaft (19) is slightly greater than that of the inner teeth (15, 16) of the inner wheels (7, 8).
 3. Shaft according to claim 1 or claim 2, characterized in that the shaft (19) is provided with an annular groove (21) near each of its ends in the region of its slots (20).
 4. Shaft according to any one of claims 1 to 3, characterized in that the inner teeth (15; 16) of the inner wheels (7, 8) are formed in adjacent end portions of the inner wheels (7, 8). 